The Development of a Multifrequency Electromagnetic Instrument for Monitoring the Phase Transformation of Hot Strip Steel

Abstract

This paper describes the development of an instrument to analyze the phase transformations of hot strip steel using an electromagnetic sensor. The sensor exploits variations in the electrical conductivity and magnetic permeability of the steel to monitor microstructure evolution during processing. The sensor is an inductive device based on a H-shaped ferrite core, which is interrogated with a multi-frequency impedance analyzer (MFIA) containing a digital signal processor (DSP). An overview of the instrument and measurements from a range of carbon steels sample are presented. The results verify the ability of the instrument both to monitor the micro-structural changes and to reject variations in liftoff distance between the sensor and the hot strip.

Measurement of microstructure changes in 9Cr–1Mo and 2.25Cr–1Mo steels using an electromagnetic sensor

“…Multi-frequency EM sensors have proved sensitive to the change of ferrite/austenite fraction [4,5], shown using model alloys, in-situ analysis and modelling, and decarburisation [6,7], shown for high carbon steels for on-line and off-line monitoring.…”

Characterization of Decarburization of Steels Using a Multifrequency Electromagnetic Sensor: Experiment and Modeling

“…Microstructures from each sample were examined by optical microscopy after sectioning, polishing, and etching using 2 pct nital. A multifrequency EM sensor, described fully elsewhere, [7,8] was used to determine variations in inductance as a function of the decarburization depth. The samples were measured by inserting them into the aircored cylindrical sensor, which had a length of 10 mm and a diameter of 20 mm and was driven using an impedance analyzer at frequencies from 10 to 10 6 Hz.…”

Electromagnetic evaluation of the microstructure of Grade 91 tubes/pipes

“…Multi-frequency EM sensors have proved sensitive to changes in ferrite (a)/austenite (g), shown using model alloys, in-situ analysis and FE based modeling software [10,11]. Prototype EM sensors are being used for in-situ monitoring of the g/a transformation during steel processing [12].…”